Electroadhesion apparatus



Dec. 24, 1935. I RAHBEK 2,025,123

ELECTRO ADHES I ON APPARATUS Filed Nov. 3, 1932 Fig. 1

Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE w Application November 3, 1932, seriai No. 641,030

, In Denmark November 10, 1931 v 9 Claims. (Cl. 179-108) This invention relates to a method and appara tus utilizing'the electrostatic attractionffor electro-adhesionpro'duced by the passage of electric current through contactingsurfaces of a semiconductor in contact with a semiconductor or a conductor.

From prionpatents, particularly U. S. Patents No. 1,533,757, and No. 1,446,748, it is known that certain substances, called semiconductors, for example agataslate, certain kinds of wood and pa per, gelatine'etc. exert: a considerable attraction mutually or to conducting bodies in contact therewithjwhen a suitable electric current is directed through the surfaces of contact. The attraction depends on the potential drop, produced by the flow of current, throughgthe contacting surfaces, and increasesfgreatly with increasing voltage. The attraction is moreover accompanied by a frictional. resistance' of, proportional magnitude, which tends .to prevent relative ,tiisplaceme'n't 'of the tw'osurf: es. v

Attempts have been made to utilize this effect in the technical-arts in various ways such .as by employing the electrostatic attraction or electro-adhesion ,produced at the'contacting surfaces for moving one'of the parts of the device towards the "other one; Electroscopes, relaysor other devices may be constructed onthis principle. It has 'alsobeen attempted, by moving mechanically the parts of the device, relatively to one another, and in such a manner that they were constantly in contact along a portion of their surfaces, to utilize the varying friction developed therebetween Ior'the construction of electromechanical devices. In this way and by the use of a very small current (a fractional part of a milliampere) it is possible to release considerable mechanical tractive forces. This effect is readily obtainable by constructing one of the contacting members in the form of a rotary cylinder or disk, the other contacting member having the shape of a band or disk maintained in contact with the rotary member by means of a resilient force or otherwise.

Such devices would appear to be of utility in the construction of simple and cheap telegraph, telephone, osclllograph and other apparatus. These compared to known constructions for similar purposes would have the very considerable advantage that the activating mechanical forces need not be furnished by electric currents, but could be provided by a motor, a clockwork or the like,' while the electric current required for governing these forces would remain quite small.

While the technical uses based upon this principle appeared at the outset to possess great possibilities, experience in the laboratory has revealed important practical diflic'ulties in that the electro-adhesion apparatus employedaltered its properties during operation for relatively short 5 periods (hours or days) .v Especially the active surfaces were altered to 'suchfan extentthatthe attracting force, on which the entire usefulness is based, either decreased considerablytor became extraordinarily great, and in either case the pracl0 tical utilityof the device was destroyed.

Attempts were madecto remedy this drawback by a special treatment of the surfaces with cleaning means, partlyof mechanicaland partly of chemical nature, but all attempts to devise conl5 structions'adaptedv to operate successfully for longerperiods were frustrated.

Continued experiments and researches of the conditionshere referred to have jnow shown that the'change undergone iby thefdevicesiin conse- 20,

quence of .theb'ssage 'of the gun-em must be assumed to be due to electrochemical alterations. lhe present invention has for its -object to avoid the occurrence of electrochemical alterations in the device owing tothe .passage ofthe 25 current,.in suchja' manner that the'device will retain the properties of value to the uses concerned, and the practical usefulness will be socured.

According to the invention this object is at- 30 tained by passing only alternating current through the device, and in such a manner that any surplus of electrochemical action in one or the other direction will be avoided entirely. Practical experiments have shown that for. attaining this 85 result it is not suflicient merely to use alternating current, but it will be necessary to secure such a wave shape'for the alternating current that the changing electrochemical effects originating from the positive and the negative impulses will coun- 40 terbalance one another entirely. This result can be attained in several manners.

In the drawing:

Figs. 1, 2, 4, 6 and 8-10 show diagrammatically various arrangements and circuits for obtaining 45 the desired mode of operation in accordance with the present invention, while; 7

Figs. 3, 5 and 7 illustrate characteristics of current curves showing the wave shape resulting from operation with the arrangement of Figs. 2, 4 and 6.

Fig. 1 shows a circuit arrangement for preventing a device consisting of a semiconductor I and a metal ribbon 2 disposed thereon from being altered by electro-chcmical changes due to rotary commutator devi there is inserted in theconnecting wires between the electro-adhesion -device I, 2 and an alternating-current generator 3, a condenser 4 of sumciently high insulating resistance, for instance a mica condenser; The condenser 4 prevents the passageofdirect current, which might otherwise be produced as a result of the inherent rectifying tendency .of the device and the morepr iess'generaliy occurring asymmetrical shapeof thealternating current wave.

In fact x-ma m n? rev at -a i c m rent from "throughthedevi emayhe'pm "alsobe at tainedby utilization oi a suitablgwave shape for,

ployed. This result may for instau the alternating current. flfhelyarying voltage, however. involves use ofa varying tractiv e force and frictional' 'eiiect between thej coiita cting sur' Kit is desired toeequalizej faces of the device. i lsa .ira ti e .ta ce. thereby n xzq a .v various jmethods'miaybeusedgand some of ,these i ibem n ia e? iii I; I i, The arrangemerit'sh wn 65 yi tli td gi a atine cu e the (114 feet. "th 'w s e' iv' bmf Td fe -l meme e; he haemi r n.

t "l .iv be arcane curve ofw l 1i ch' 1 s tn fa ai ma f ndwn in F 1 'Y. Ba hah e ve feltfaq i force which'is very nearly 'as iinifo'rn i asjthatow with-thepoiaiinngbattery ai The 'arnr 20 can b"movedf-byacam'disk'fiifii connection with a spring 24. "FigQ-S'sho'withelshape of curvefo'r' the polarizing voltageV attained with thisarrangement. By'adiustment of the battery con nection 25 and by alteration of thes hape of the cam disk '23, the amplitude aswell ,as the "duration of the oppositely poled voltage impulsesfcan be varied.

In the'arran'gementshown in Fig 6, the electro-adhesion device I, 2 is connected-to a potentiometer I inserted in a circuit which contains a seriesreslstance 8. a glow discharge valve 9 arranged in'parallel to the potentiometer 1, and the secondary of a transformer l0 supplied with current from an alternating current generator I i. The discharge valve 9 when lightedwill produce a drop of voltage in the series resistance, and will itself remain at a voltage'situated in the vicinity of the lighting voltage, whereby'for the alternating voltage V impressed upon'the device I, 2 will have the angular wave shape shown by full lines in Fig. 7. the dotted wavetops V indicating the alternating voltage of the generator, and the voltage V" indicating the glow discharge voltage of the valve. or a fractional part thereof determined by the adjustment of the potentiometer. With such a shape of curve the attracting force'produecd betweenthe parts of the device is essentially more uniform than with a pure sinusoidal wiiuge.

lly the use of polymhase currents there results the passage .of the electric current. To this end,

a considerable equalization of the tractive force and, thereby, considerably increased attraction and frictional forces between the parts of the device. Fig. 8 shows by way of example a device in which a two-phase alternating current is used, 5 the phases of which are mutually displaced by 90. From a transformer (2 the current is directed to suitably proportioned serially connected condenser i3 and resistapce,ldz wnereby in the mannerknownflper s e two voltages' df equal mag- 10 nitude b'utlphase-displaced by 90 relatively to one another'are obtained. These voltages are supplied respectively to the upper and lower portionsof the'device I, 2, which,v in the example shown; oonsistspt a semiconductor l and two conductor s {disposedon an insulating supporting plate 'iind connted, separately through con- "densers' ,"tdthe circuit consisting of the transformerjlhthe condenser l3 and the resistance (4.

hew a yi e n we sbthrsame a strips il l f aati ifii i alt afi bqmfiaibate is orie'part'ofthedevi wliilethe other part at i l. 1-. Thei 'me trips; ar hhegt rssre v vii fir uz m denser'l to individual phases of "a 'Y- coniie'cted t r -P l nat ns, r m e n mt gj ing its neutralior'gietugn ieadicohpectea to conductor l.iThe' atti acti on s betweenj the metal j a i' e' 'e l' bn fl ta t b ea equalized by this con tellati n, duetqtheirphase an displacements "whieha r ef'such"that as the tractive force at one strip decreasesfit'increas'e's at others.

"If '15 desired;by'nieans dithe'frictional force produced in thedeYice, to cause ai'dia'phragm or recording 'p'e'n-o'r t' e lilreto inove'synchronousiy 3.!

' two-phase current gamma runway-panam a a. lso "the attraction} is nia'ximuxn inifine of the devices fwhen "it iszer'ojin the other o'r'lfe, the two metal ribbonsz will'move the diaphragm now to one and now to the other. sidein synchronism with the alternating current, and the membrane will produce a tone, the frequency of which is twice as high as the number of periods of the 65 alternating current? I claim: 1

1. In a device utilizing electro-adhesion between contacting surfaces of substances traversable by electric current. the method of operation which comprises, passing through said surfaces an alternating current of angular wave shape thereby to minimize fluctuations in the resulting tractive forces between said surfaces while preventing the occurrence of permanent electrochemical alterations in said device.

2. In-a device utilizing electroadhesion between contacting surfaces of substances traversable by electric current, the method of operation which comprises, passing through said surfaces an alternating current of substantially rectangular wave shape thereby to minimize fluctuations in the resulting tractive forces between said surfaces while preventing the occurrence of permanent electrochemical alterations in said device- 7 3. In an electro-adhesion device including conductive bodies having surface in contact, a source of alternating voltage connected to said bodies and means adapted to prevent the flow oi detrimental direct current through said bodies.

4. In an electro-adhesion system including conductive substances having surfaces in contact, a source of alternating voltage, a connection for applying said voltage to said device, and a condenser serially interposed in said connection.

5. In an electro-adhesion system according to claim 3, the alternating voltage applied being of angular wave shape.

6. An electro-adhesion system comprising a first conductive element having a surface arranged to contact simultaneously with surfaces of a plurality of conductive elements mounted in insulated relation, a poly-phase voltage source having a common return, and connections extending respectively from said common return to said first conductive element and from individual phases of said source to said elements insuiatedly mounted.

7. An electro-adhesion system according to claim 6 wherein condensers are interposed in said connections from said individual phases.

8. In an electro-adhesion device adapted to be controlled by varying electric currents and comprising at least two bodies of substances traversable by said currents and contacting each other, means for applying an alternating current besides the controlling current to said bodies, said alternating current being of other than ordinary sinusoidal shape and its positive half-waves being adapted to extinguish any electrochemical effect of its negative half-waves, and vice versa.

9. In an electro-adhesion device adapted to be controlled by varying electric currents and comprising at least two bodies of substances traversable by said currents and contacting each other, means for applying an alternating current besides the controlling current to said bodies, said altematlng current being of other than ordinary sinusoidal shape and its positive and negative half-waves being essentially symmetrical.

KNUD RAHBEK. 

